Adding Multiple Documents

In order to do more interesting things with queries, let's add multiple
simple documents to the collection. These documents will just be of the form
array( "i" => value ); and we
can do this fairly efficiently in a loop:

Notice that we can insert arrays with different keys into the same
collection. This aspect is what we mean when we say that MongoDB is
"schema-free". In the example above each document has an
i field, but also a field name in the form of
field + $i.